PROJECT SUMMARY Anxiety disorders can be severely debilitating, are prevalent in females, and represent a significant public health burden. These disorders often begin with early-life dispositional anxiety that can lead to the development of anxiety and depressive disorders and co-morbid substance abuse. New treatment strategies aimed at early-life anxiety are needed and have the potential to prevent this life-long suffering. The nonhuman primate (NHP) model of early-life anxious temperament (AT) is ideal because of similarities between rhesus monkeys and humans in the development of socio-emotional behavior and its underlying neural circuits. Our work, and that of others, strongly implicates altered function of the extended amygdala as a core feature of AT and anxiety disorders. The extended amygdala includes the central nucleus of the amygdala (Ce) and the bed nucleus of the stria terminalis (BST). The extended amygdala integrates threat-relevant information from cortical and subcortical inputs, and initiates behavioral and physiological responses to threat. Of particular interest are the orbitofrontal ?regulatory? influences on extended amygdala function and anxiety. In considering the development of new treatments, there are a number of critical questions. Advances in molecular technologies for reversibly and bi-directionally controlling brain function are beginning to make some of these questions tractable. Designer receptors exclusively activated by designer drugs (DREADDs) are ideal for examining early-life AT in NHPs because they can modulate critical brain regions for long periods of time (i.e. hours) -- particularly relevant for uncovering mechanisms related to mood and anxiety dysregulation. The DREADDs technique involves infecting a brain region with a viral vector that expresses a receptor that does not naturally occur in the brain, which is then combined with a pharmacological intervention, an otherwise ?inert? drug that selectively activates DREADDs. Importantly, DREADDs can be used to chronically alter circuit function to model long-term brain alterations associated with psychopathology. We established a Cre-Lox recombination strategy to express DREADDs in NHP amygdala neurons that project to select effector sites. This allows unprecedented control of specific projections in the brains of freely behaving NHPs during exposure to ethologically relevant contexts. This proposal will use DREADDs in young female NHPs to understand how, early in life, projections in the extended amygdala drive sustained anxiety-related behavior and how this circuit is modulated by direct projections from caudal orbitofrontal cortex. It will also explore whether chronic early-life activation of the Ce is sufficient to induce extreme anxiety accompanied by the functional and structural brain changes associated with stress-related psychopathology. Lastly, the proposed studies will identify molecular markers of projection-specific anxiety-modulating neurons that will enable development of selective circuit-based treatment approaches. Together these studies will set the stage for the feasibility of amygdala projection-specific treatments for early-life anxiety, and demonstrate the utility of an animal model to test these novel approaches.